An evolutionary approach to develop durable disease resistance to bacterial canker of cherry

通过采用高密度种植，英国樱桃产量从2000年的400吨恢复到2014年的3500吨，导致由假单胞菌引起的细菌溃疡病成为樱桃的主要疾病，对此没有有效的控制。我们最近的工作表明，细菌溃疡病不是由单一的细菌种群引起的，而是由三组不同的假单胞菌引起的，每一组都独立地获得了在樱桃上引起疾病的能力，并且每一组都以微妙的不同方式操纵宿主，以破坏植物防御并与树长期共存。这种现象被称为趋同进化，是一个有趣的发现，因为它产生了几个基本的科学问题。在这项提案中，我们试图回答四个问题，基于最近对这种商业上重要但尚未充分研究的病原体的研究。首先，樱桃疫霉在樱桃上生态位生存和持续存在的基础是什么？我们希望了解，如果不同的毒素，效应物（一类特殊的蛋白质分泌的病原体，参与抑制植物免疫和促进病原体生长）和其他基因簇，参与操纵宿主防御，决定生存能力在特定的壁龛（例如在木本组织）或在特定的时间，一年中，这些是否是不同的，在我们的三个假单胞菌分支？第二，宿主特异性是如何由效应物含量决定的？保守的效应，过度代表收敛进化的假单胞菌群相比，密切相关的非樱桃或李病原体，在适应这些主机发挥了重要作用？这种进化的方法，整合来自许多不同菌株的假单胞菌的信息是一种新的方式，利用分子进化的模式，以提供洞察哪些病原体基因是进一步研究的重要目标。解决这两个问题将为病原体如何进化到其宿主上提供基本的见解，并可能在考虑如何在现场控制这些病原体时提供新的途径。第三，哪些效应子控制樱桃中已知的抗性反应？这是一个至关重要的问题。植物免疫系统的一部分由特定类别的基因（广义上称为抗性或R基因）控制，这些基因已经进化为编码识别病原体攻击的蛋白质，通过监测效应子的存在或活性，然后快速激活植物防御反应。效应子通常被称为病原体的阿喀琉斯之踵，因为它们都是致病性所必需的，但使病原体容易被检测到。了解樱桃材料中识别哪些效应子对于预测特定植物抗性的可能有用性是重要的。例如，在病原体群体中以低频率识别罕见效应子不如识别高度保守效应子的R基因有用，所述高度保守效应子是致病性所必需的。我们的方法旨在鉴定针对所有樱桃感染假单胞菌菌株所共有的效应子的抗性基因，以及其他先前鉴定但未表征的抗性。第四，樱桃抗疫霉的遗传结构是什么？通过识别樱桃基因组中控制抗性的区域，使用一种称为遗传作图的技术，标记R基因的分子标记可以被英国工业开发和使用（植物育种家）为了培育对所有三组致病假单胞菌具有抗性的樱桃品种。回答这些问题为植物育种家提供了他们开发抗性品种、提高产量、质量和行业的盈利能力，并减少供应链中的浪费。

The resurgence of cherry production in the UK from 400 tonnes in the year 2000 to 3500 tonnes in 2014, achieved through the adoption of high-density plantings, has led to bacterial canker, which is caused by Pseudomonas syringae, becoming the main disease of cherry, for which there is no effective control. Our recent work has shown that bacterial canker is not caused by a single bacterial population but by three distinct groups of Pseudomonas, each having independently acquired the ability to cause disease on cherry and each manipulating the host in subtly different ways in order to subvert plant defences and survive in long term associations with the tree. This phenomenon is termed convergent evolution and is an interesting finding, as from it several fundamental scientific questions arise. In this proposal we seek to answer four questions, based upon recent research into this commercially important, yet understudied, pathogen. First, what is the basis of niche survival and persistence of P. syringae on cherry? We wish to understand if different complements of toxins, effectors (a special class of proteins secreted by the pathogen that are involved in suppressing plant immunity and promoting pathogen growth) and other gene clusters, implicated in manipulation of host defences, determine survivability in particular niches (in woody tissues for example) or at particular times of year, and whether these are different in our three Pseudomonas clades? Second, how is host specificity determined by effector content? Do conserved effectors, over-represented in convergently evolved Pseudomonas groups when compared to closely related non-cherry or plum pathogens, play an essential role in adaptation onto these hosts? This evolutionary approach, integrating information from many different strains of Pseudomonas is a novel way of utilising patterns of molecular evolution to provide insights into which pathogen genes are important targets for further study. Addressing these two questions will provide fundamental insights into how pathogens evolve onto their hosts and may provide new avenues to pursue when considering how to control these pathogens in the field. Third, which effectors control known resistance responses in cherry? This is a crucial question. Part of the plant immune system is controlled by specific classes of genes (broadly termed resistance or R genes) that have evolved to encode proteins that recognise pathogen attack, by monitoring for the presence or activity of effectors and then rapidly activating plant defence responses. Effectors are often referred to as the pathogen's Achilles heel, as they are both required for pathogenicity but leave the pathogen vulnerable to detection. Understanding which effectors are recognised in cherry material is important to predict the likely usefulness of particular plant resistances. For example, recognition of a rare effector at low frequencies in a pathogen population is less useful than an R gene that recognises a highly conserved effector, essential for pathogenicity. Our approach seeks to identify resistance genes that target effectors that are common to all strains of cherry infecting Pseudomonas, as well as other previously identified, but uncharacterised, resistances. Fourthly, what is the genetic architecture of resistance to P. syringae in cherry? By identifying the regions of the cherry genome that control resistance, using a technique called genetic mapping, molecular markers tagging R genes can be developed and used by the UK industry (plant breeders) in order to breed cherry cultivars resistant to all three groups of pathogenic Pseudomonas.Answering these questions provides plant breeders with the information that they require to develop resistant cultivars, improving yield, quality and the profitability of the industry and reducing waste in the supply chain.